This invention relates to fin pack heat exchangers and, in particular, to apparatus for facilitating the hairpin tubes into a fin pack unit.
As disclosed in the U.S. Pat. Nos. 4,195,540; 4,285,256 and 4,286,486, machines have recently been developed for automatically stacking prestamped plate fins into packs of the type used in heat exchanges for refrigeration systems or automotive cooling systems. The plate-like fins are stamped from sheet material and the fins are brought to an endless conveyor for stacking. The conveyor includes a series of laterally disposed blocks having elongated spikes or mandrels capable of passing through tube receiving holes formed in each of the plates. The plates are loaded upon the mandrels one over the other to form a vertical column defining a fin pack unit. The units are assembled on an upper horizontal reach of the conveyor and are removed at the end of the reach as the stacking blocks swing into a horizontal position during the return portion of the conveying cycle.
The assembled fin pack units, upon being removed from the stacking machine may be passed on to an automatic assembling machine wherein the end baffels or "tube sheets" are registered over the top and bottom of each stack and hairpin tubes then laced through the assembly. The term hairpin tube, as herein used, refers to a U-shaped tubular member having two equally elongated legs that are in general parallel alignment. When the hairpin tubes are laced into a thin pack assembly, each leg forms a flow channel that is perpendicular to the fins. The legs of adjacent hairpins are later interconnected by means of tube bends to complete the flow circuit through the fin pack unit. The open ends of the hairpin are generally belled and the tube bends inserted into the bell openings and soldered in place to provide a fluid tight joint. Prior to inserting the tube bends into the bells, the hairpin tubes are also expanded into locking contact against the fins by passing an expanding rod through the tube legs. An automatic machine for lacing hairpins into assembled fin pack units is described in U.S. Pat. No. 4,228,573 which issued to Barnard.
Although automatic machines have been devised for performing many of the tasks involved in the manufacture of fin pack coils. Typically each hairpin is formed of an aluminum based material that is cold worked into a U-like configuration. The two legs of the U-bend are relatively long and as a consequence, the alignment between the tube ends varies dramatically between hairpins. With the center distance between the two legs being typically wider than the center distance between the tube holes formed in the fin pack units. Inserting the hairpins into the pack thus poses a very special problem. In the above noted Barnard machine, the fin packs are laid upon their sides and the hairpins are inserted horizontally into the receivng holes. To align the tubes with the holes, the hairpins are laid in a row in a side by side relationship within a special fixture immediately adjacent to the fin pack unit. An entire row of hairpins is then pushed into the fin pack. The horizontal loading and lacing of the hairpins in this manner is time consuming, requires a good deal of space and raises very special handling problems involving both aligning the tube ends positively with the fin pack holes. Laying the individual tubes into the holding fixture is ordinarily performed by hand and this subject to human error. If the hairpins are not accurately aligned within the fixture the tubes will hang up during the insertion process.